Envigo uses well-established techniques to successfully produce time mated rats, mice, hamsters, and rabbits. We use an impedence meter for determining the stage of estrus in rats prior to breeding. Time mated rats and mice are determined by observation of a vaginal plug. Plug date is considered to be day zero (0) of gestation.

Due to the natural variation in the length of gestation, the exact day of parturition cannot be guaranteed. In addition, Envigo cannot guarantee the minimum number of offspring per litter.

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Envigo will not ship animals which are in the last stage of gestation, as they may deliver their litter prematurely while in transit, and depending on the circumstances involved, requests for credit or replacement of these animals may be declined at our sole discretion.

If problems regarding gestational age or pregnancy are encountered, customers should immediately contact Envigo’s customer service department and provide detailed information regarding the animals involved.


Expected pregnancy rate
Stock or strain Timed mated <13 days gestation (at shipping) Timed mated ≥ 13 days gestation and over (at shipping) Untimed pregnant ≥ 13 days gestation (at shipping)
Outbred mice / rats * 90% 90% **
Inbred mice / rats * 90% 90% **

* Plug guarantee only; no guaranteed pregnancy. Plug date = Day 0.

** Untimed pregnant rodents will be selected from our breeding colonies on the basis of palpation or visual confirmation. A variation of three to four days gestation can be expected. Therefore Envigo cannot be held responsible for actual gestation and/or exact day of littering.

To avoid charges, cancellations for timed mated animals must be received one week prior to mating date.

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